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Abstract

We theoretically study the role of dispersion in propagation of rotating beams in left-handed materials (LHMs). By modeling the rotating beam as a superposition of two rotating Laguerre-Gaussian beams with opposite chirality, same magnitude and different frequencies, we demonstrate that the rotation property of the rotating beam in LHM is significantly dependent on the sign and strength of dispersion: In the normal dispersion region, the direction of transverse energy flow is reversed compared to the vacuum, due to the negative refractive index of LHM, while in the anomalous dispersion region it may be parallel or antiparallel to that in the case of vacuum, depending on the strength of dispersion. In addition, we find that the angular momentum density can be parallel or antiparallel to the transverse energy flow in LHM, while the angular momentum flow is always opposite to the transverse energy flow.

Figures (4)

Evolution of the interference pattern of model spiral beams viewed against the beam propagation direction in the waist plane. The white dot indicates the rotation of the pattern due to the azimuthal index of two-term superposition of LG beams. Here, Ω is the angular velocity of interference pattern, T = 2(l+ - l-)π/Δω is the period of rotation. (a)-(d) superposition LG0,+1 +LG0,-1: we know that Ω > 0 and the interference pattern exhibits anticlockwise rotation. (a’)-(d’) superposition LG1,-1 +LG1,+1: we get that Ω > 0 and the interference pattern exhibits clockwise rotation.